Quikrete is concrete -- a mix of Portland cement, sand and gravel (and a setting accelerator). But for your vermiculite concrete you want to use pure Portland cement (not concrete). Think of it this way -- when you make insulating concrete, vermiculite replaces the sand and gravel as the aggregate that you mix with Portland cement.

You can buy Portland cement by the bag at Home Depot and it isn't expensive.
James

__________________ My geodesic oven project: To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts., To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

The concern is that the presence of aggregate in the mix (assuming that it is a dry concrete mix rather than just a fast setting cement) will greatly reduce the insulating properties of the layer. If this is the case you can either remove and relay or maybe add a further insulating layer over the top, as long as that wouldn't make your oven too high.

At my home depot they sell ALL of the broken bags of concrete products for $4.10 - I do mean all - if they have six broken bags its just $4.10 TOTAL I used stucco on the outside of my last cooker and got two bags plus seven quick crete for $4.10 That stuff is $17 per here in FL. - what a bonus if you have a way to transport.

I know you will hate to hear this.. but I think you need to redo it. Or form another insulating layer on top. I think what you have now will simply wick your heat out. And your firing times will be long, and your wood consumption will be high. It will cost you in the end.

The insulating layer should be 5 parts verm to 1 part Portland cement and just enough water to hold it all together. Mix the dry ingredients first, then slowly add water until you can just squeeze a little water out the mixture with a closed fist.

I have a 3.5 - 4 inch layer of the vermcrete under my oven, and I wish I would have built it up to 6 inches or more.

Just my opinion, but I'd hate to see you build an oven that is hard to use, under cooks the bottoms of your pizzas, and burns the tops.

While I am new to this site I am not new to the heat and insullation concept. Heat rises! I think that a firebrick bottom with any form of concrete base should work if the top is thick enough. The purpose of curved oven tops and in a fire place angled sides is to radiate heat. My own oven / smoker / grill has seven inches of foundation then firebrick on the bottom. I used full firebricks for the box with 4 or 5 inches of cement / vermiculite a layer of cardboard for expansion then solid concrete. My weakest link is I have an actual flue thats 13 X 17 for heat to escape. I have a way to neck that down or close it with firebrick. In about a month I will be able to try the oven. It is new and I don't want to crack anmything. Plus it is to hot outside (FL) Pictures posted yesterday

No part of this website or content thereof may be reproduced, distributed or transmitted in any form or by any means, nor may any part of this website be stored in a database or other electronic retrieval system, or any other website, without the prior written permission of Forno Bravo.